Fuel element storage tank for nuclear power plants

ABSTRACT

To avoid the escape of radioactive aerosols from the water surface of a fuel element storage tank, a continuous overflow of the water is maintained together with an air curtain disposed closely above the water surface.

United States Patent Schettler et al.

1 1 Apr. 30, 1974 FUEL ELEMENT STORAGE TANK FOR NUCLEAR POWER PLANTSInventors: Kurt Schettler, Schronfeld 79;

Hermann Kuster, Anton-Bruckner Str. 20, both of Erlangen, Germany Filed:July 8, 1971 Appl. No.: 165,845

Foreign Application Priority Data July 9, 1970 Germany 2034087 U.S. C1.220/85 R, 250/108 R Int. Cl. B65d 25/00 Field of Search 220/85 R, 85 VR,85 VS, 220/88 B, 45; 250/108 R, 108 WS, 106 R; 206/1 R References CitedUNITED STATES PATENTS Allen 250/108 WS 3,179,243 4/1965 Ashcroft 206/1 R3,229,096 1/1966 Bonilla ct a1 250/108 R 3,230,373 1/1966 Montgomery..."250/108 R 3,414,727 12/1968 Bonilla 250/108 R 3,432,666 3/1969 Nash eta1. 250/108 R 3,483,380 12/1969 Antonsen et al.. 250/108 R PrimaryExaminer-Samuel B. Rothberg Assistant Examiner-James R. GarrettAttorney, Agent, or FirmHerbert L. Lerner [57] ABSTRACT To avoid theescape of radioactive aerosols from the water surface of a fuel elementstorage tank, a continuous overflow of the water is maintained togetherwith an air curtain disposed closely above the water surface.

9 Claims, 2 Drawing Figures FUEL ELEMENT STORAGE TANK FOR NUCLEAR POWERPLANTS The invention relates to a water-filled tank contain ing fuelelements for nuclear power plants and, more particularly, to fuelelement storage tanks or flooded reactor chambers wherein, according tothe power of the reactor, the water is more or less intensely heated.With increasing water temperature, the amount of water evaporating fromthe storage tank increases so that the likelihood of an undesired escapeof highly radioactive aerosol must be taken into account.

Attempts have been made to prevent or at least obstruct the escape ofradioactive vapors and mists from fuel element storage tanks by placingcovers above the water level. In this regard, both solid coverings inthe form of foils, jalousies, etc. as well as liquids, which float onthe surface of the water due to their relatively low specific weighthave been proposed. However, the use of such coverings have thedisadvantage that the accessibility of the fuel elements is impededthereby and that, moreover, when inserting and removing the fuelelements, the respective coverings must be partly or entirely removed.

Consideration has also been given heretofore to providing air suction orsimilar pneumatic devices to intercept or capture escaping aerosolstherewith and render them harmless. If such measures are to have thedesired results, attention must be given to the fact that, due to therespectively strong suction, turbulent air currents are produced whichcause the formation of waves or ripples on the water surface. Thiscondition is disadvantageous in that the view from above through thewater surface to the fuel elements reposing in the water is impeded orprevented. This presents a considerable disadvantage because the fuelelement rods cannot therefore be reliably gripped without difficulty inorder to remove them from te storage tank. Only when the surface of thewater is calm can the location of the individual fuel elements beoptically determinable without any trouble.

It is accordingly an object of the invention to provide fuel elementstorage tank for nuclear power plants which has relatively simple meansfor reliably preventing escape of radioactive aerosols from the tank.

It is a further object of the invention to provide such fuel elementstorage tank which avoids the disadvantages of the heretofore knownstorage tanks of this general type.

With the foregoing and other objects in view, there is provided, inaccordance with the invention, fuel element storage tank for nuclearpower plants comprising a walled structure enclosing a chamber forreceiving water therein up to a given overflow level and having a crownat the top thereof defining an access opening to the chamber, wateroutlet means in the walled structure below the given water level, thewater outlet means being connectible to the suction side of acirculatory pump, water overflow means provided at the water level invicinity of the crown at least two opposite locations of the chamber,the water overflow means being also connectible to the suction side ofthe circulating pump and being continously operable for all conditionsof the pump, and, also located in vicinity of the crown, first channelmeans for blowing air in flat sheets above the water level in givendirection and second channel means for withdrawing spent air at thewater level in direction opposite to the given direction so as toproduce and maintain an air curtain over the water level of the water.When the storage tank is of rectangular shape, the water overflow meansare located opposite one another along the entire breadth of the storagetank.

In accordance with another feature of the invention, the water outletmeans includes suction conduits located far below the water level andhaving inlet openings communicating with the interior of the chambermeans, the water overflow means being connected by connecting lines withthe suction conduits.

In accordance with further features of the invention, the suctionconduits are provided with means for retarding direct flow of the tankwater, the flow retarding means being automatically variable and beingin the form, for example, of pivotable flaps.

With respect to the air curtain to be maintained above the water level,in accordance with an additional feature of the invention, slit nozzlesare provided for producing laminar currents of air in flat sheets overthe water level from opposite sides of the storage tank. In substitutiontherefor or in addition thereto, there are provided, in accordance withthe invention, baffles or guide plates which force the production of alaminar air current. The air currents in the form of flat sheetsopposing one another meet substantially in the center of the storagetank above the water level whereat the suction action applied to the airbecomes perceptible. Furthermore, in accordance with the invention,openings defined by baffles or guide plates are provided for sucking theair into the second channel means while markedly avoiding the formationof turbulence phenomena, and the air being sucked through the bafflestravels substantially parallel to the overlying sheets of air beingblown into the tank and in opposite direction thereto.

ln an especially economical manner, all of the devices serving to limitor prevent the escape of radioactive aerosol, can be disposed invicinity of the crown of the storage tank in a chamber or niche providedfor the water overflow means or waterfall and simultaneously serving forcontaining the first channel means or air supply channels and the secondchannel means or air discharge channels. During all flow operations, thesurface of the water remains calm without any wave motion so that aclear optical view of the fuel elements is continously afforded fromabove the storage tank.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin fuel element storage tank for nuclear power plants, it isnevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing, in which:

FIG. 1 is a vertical sectional view of the fuel element storage tank fornuclear power stations constructed in accordance with the invention; a

FIG. 2 is an enlarged fragmentary view of FIG. 1.

Referring now to the drawing, there is shown in FIGS. 1 and 2, the upperpart of a fuel element storage tank having a wall or walls 1 and filledwith water 2. A niche or recess 8 is provided in the wall 1 in thevicinity of the tank crown 3 and is of such size as to provide adequatespace therein for accommodating accessory equipment which, in accordancewith the objective of the invention, prevents the escape of radioactiveaerosols from the surface 5 of the water 2.

To cleanse and cool the water 2 contained in the storage tank, acontinuous circulation of all the water 2 is conventionally employed forwhich purpose conduits connected to the aspirating or suction side ofanonillustrated circulating pump are provided. In addition to the suctionapplied at the inlet openings 6 of the conduits 10, waterfalls 12 of theweir overflow type are provided connecting conduits 13 leading therefromto the suction conduits 10. Part of the water in the storage tank thusruns as the respective waterfall 12 along a path through the conduit 13to the suction line 10, while another part of the water is sucked intothe respective line 10 through the inlet opening 6.

In order to ensure the maintenance of a waterfall 12 for all operatingconditions of the non-illustrated circulating pump, suitable flowretarding devices are provided within the suction line 10 in thevicinity of the inlet opening 6. In the illustrated embodiment, the flowretarding devices are in the form of movable flaps 14 which are of suchdimensions with respect to the specific gravity thereof that theythereby exert a controlling function and continually assure an adequatedraw of water through the suction conduit 10 to the nonillustratedcirculating pump without adversely effecting the waterflow 12 thereby.The water level 7 in the lower region of the niche 4 is always severalcentimeter lower than the respective level 5 of the water in the storagetank chamber proper.

In order to adjust the partial flow ofwater automatically, a differentcontrolling flow retarding device other than the flap 14, can beprovided. If disturbances occur, such as irregularities at the waterlevel regulating device or, for example, when a pump is turned on andoff due to unstable operation, assurance of a reliable water supply tothe circulating pump at the suction side thereof is alway providedthereby.

It is also of importance in accordance with the invention that thesuction and the water overflow take place at opposite sides of thestorage tank, i.e., at both longitudinal sides. in the case ofarectangular storage tank, and if possible along the entire lengththereof. If desired. a waterfall can be produced additionally at bothnarrow sides of the rectangular storage tank. When the storage tank isround, i.e., cylindrical, or oval, the waterfall can be provided aroundthe entire inner periphery thereof. The discharge of surface water on atleast opposite sides of the storage tank is advantageous inasmuch as arising or buoyant flow of the water in the central region thereof withinthe storage tank takes place due to the heat development caused by thefuel elements, so that with a circulation of the water within thestorage tank, one must expect that a rise or upward flow will occur inthe center of the water and a downwardly directed flow at the outer wallor walls 1 of the storage tank. The water thereby flows, at the surface5 thereof, from the center outwardly to the edge or edges of the storagetank chamber so that the suction through the overflow of the watersurface 5 proceeds in the same flow direction. The water surface 5thereby is maintained without any wave motion for all flow processes sothat a clear optical view from above of the fuel elements in the storagetank is continually provided.

Furthermore, due to the withdrawal of the water at the surface 5 from atleast two opposite sides of the storage tank, all floating substancespresent therein are removed in a very short time and filtered eventuallythrough a non-illustrated water purifying system.

Simultaneously with the self-cleaning of the water surface 5 by overflowthereof on at least two opposite sides of the storage tank, means arealso provided for producing a curtain of air above the water surface 5by blowing air in laminar flow flatly over the water surface from atleast two opposing sides of the storage tank. The air is suppliedthrough conduits 8 into an upper region of the niche 4 where arespective air chamber 9 with suitable outlet nozzles or baffles (guideplates) 15 are provided in order to ensure a laminar flow of airtherefrom. The initially tightly bunched together air current travelingin direction of the arrows 11 fans out only above the center of thestorage tank in the region 17.

Simultaneously with the introduction of the air above the water level 5through the nozzles or baffles 15, several centimeters therebeneath, theair is withdrawn from above the water level 5 through baffles 16,located laterally along the same length as the nozzles or baffles l5,and is exhausted through the air discharge channel 22 and the airdischarge conduits 20. Due to the blocking or retarding action of thenozzles or baffles 15 in the vicinity of the air supply chamber 9, aswell as guides or other devices 21 at the spent air discharge chamber22, the discharging spent air is mainly withdrawn only from the centerregion 17 in direction of the arrows 18. As a result of the considerablygreater range or radius of action of the blown out jet of air ascompared to an air displacement produced only through suction action, itis possible to manage with exceptionally small quantities of air and lowair pressures. Aerosol discharge into the room atmosphere is therebyvirtually eliminated. By locating the air supply and discharge channels9 and 22 together with the device of the tank overflow or waterwalls 12as well as an emergency discharge line 19 in a common niche 4 formed inthe crown 3 of the storage tank, a relatively simple embodiment of astorage tank can be produced which is economical both as to cost and asto the space occupied thereby.

We claim:

1. Fuel element storage tank for nuclear power plants comprising awalled structure enclosing a tank chamber for receiving water therein upto a given overlfow level and having a crown at the top thereof definingan access opening to said tank chamber, water outlet means in saidwalled structure below said given water level, said water outlet meansbeing connectible to the suction side of a circulating pump, wateroverflow means provided at said water level in vicinity of said crown atat least two opposite locations of said tank chamber, said wateroverflow means being also connectible to the suction side of thecirculating pump and being continuously operable for all conditions ofthe pump, and, also located in vicinity of said crown, first channelmeans for blowing air in flat sheets above the water level in givendirection and second channel means for withdrawing spent air at thewater level in direction opposite to said given direction so as toproduce and maintain an air curtain over the level of the water.

2. Fuel element storage tank according to claim 1 wherein said wateroutlet means includes suction conduits spaced downwardly from the waterlevel and having inlet openings communicating with the interior of saidtank chamber, said water overflow means being connected by connectingconduits to said suction conduits.

3. Fuel element storage tank according to claim 2, wherein said suctionconduits are provided with means for retarding direct flow of the waterin said tank chamber.

4. Fuel element storage tank according to claim 3 wherein said flowretarding means are automatically variable.

5. Fuel element storage tank according to claim 4 wherein said flowretarding means are in the form of pivotable flaps.

6. Fuel element storage tank according to claim 1 wherein niches areformed in said walled structure in vicinity of said crown thereof, saidniches having means for receiving water therein from said water overflowmeans and including, respectively, a fresh air chamber for receivingtherein the air being blown into said tank chamber and a spent airchamber for receiving therein the spent air being withdrawn from saidtank chamber.

7. Fuel element storage tank according to claim 6 wherein said fresh airchamber is provided with outlet nozzles for producing an air flowdirected in flat sheets above the level of the water in said tankchamber.

8. Fuel element storage tank according to claim 6 wherein said fresh airchamber is provided with baffled openings for producing an air flowdirected in flat sheets above the level of the water in said tankchamber.

9. Fuel element storage tank according to claim 6 wherein said spent airchamber is provided with spent air inlet openings, and guide means forguiding the spent air through said spent air inlet openings whilepreventing the fresh air being blow into said tank chamber from beingdirectly withdrawn through said spent air inlet openings.

n l a

1. Fuel element storage tank for nuclear power plants comprising awalled structure enclosing a tank chamber for receiving water therein upto a given overlfow level and having a crown at the top thereof definingan access opening to said tank chamber, water outlet means in saidwalled structure below said given water level, said water outlet meansbeing connectible to the suction side of a circulating pump, wateroverflow means provided at said water level in vicinity of said crown atat least two opposite locations of said tank chamber, said wateroverflow means being also connectible to the suction side of thecirculating pump and being continuously operable for all conditions ofthe pump, and, also located in vicinity of said crown, first channelmeans for blowing air in flat sheets above the water level in givendirection and second channel means for withdrawing spent air at thewater level in direction opposite to said given direction so as toproduce and maintain an air curtain over the level of the water.
 2. Fuelelement storage tank according to claim 1 wherein said water outletmeans includes suction conduits spaced downwardly from the water leveland having inlet openings communicating with the interior of said tankchamber, said water overflow means being connected by connectingconduits to said suction conduits.
 3. Fuel element storage tankaccording to claim 2, wherein said suction conduits are provided withmeans for retarding direct flow of the water in said tank chamber. 4.Fuel element storage tank according to claim 3 wherein said flowretarding means are automatically variable.
 5. Fuel element storage tankaccording to claim 4 wherein said flow retarding means are in the formof pivotable flaps.
 6. Fuel element storage tank according to claim 1wherein niches are formed in said walled structure in vicinity of saidcrown thereof, said niches having means for receiving water therein fromsaid water overflow means and including, respectively, a fresh airchamber for receiving therein the air being blown into Said tank chamberand a spent air chamber for receiving therein the spent air beingwithdrawn from said tank chamber.
 7. Fuel element storage tank accordingto claim 6 wherein said fresh air chamber is provided with outletnozzles for producing an air flow directed in flat sheets above thelevel of the water in said tank chamber.
 8. Fuel element storage tankaccording to claim 6 wherein said fresh air chamber is provided withbaffled openings for producing an air flow directed in flat sheets abovethe level of the water in said tank chamber.
 9. Fuel element storagetank according to claim 6 wherein said spent air chamber is providedwith spent air inlet openings, and guide means for guiding the spent airthrough said spent air inlet openings while preventing the fresh airbeing blow into said tank chamber from being directly withdrawn throughsaid spent air inlet openings.